1. Field of the Invention
The field of this invention pertains to communications and, more particularly, to a means for transferring information within a mobile communication system.
2. Description of the Related Art
Digital communication systems have become increasingly popular for many applications. One advantage of a digital communication system is the flexibility to carry many different types of information over a single system. A single digital communication system may be used, for example, to transmit digitized sound, text, computer data, digital video, or other information existing in digital form.
To achieve flexibility, a communication system may be designed to transfer digital information from one end user to another in a transparent fashion. The communication system then operates as a transparent data pipeline for one or more other systems which are called application end users. Each application end user connected to the communication system generally has the responsibility for ensuring that the data ultimately delivered is in a form which is properly recognized by the user.
To better achieve such flexibility, it has been suggested that a communication system be designed with a layered architecture. One example of a general layered architecture for digital communication systems is the International Organization for Standardization (ISO) Reference Model for Open Systems Interconnection ("OSI Reference Model"). The OSI Reference Model has been adopted as an international standard by the ISO and by the International Telephone and Telegraph Consultative Committee (CCITT).
FIG. 4A is a diagram showing the OSI Reference Model 401. The OSI Reference Model 401 comprises a communication system having seven layers which form a communication path between a first end user 405 and a second end user 410. The seven layers may be divided into two sets--a set of upper layers 415 and a set of lower layers 420. The upper four layers 415 normally reside in the application end users desiring to communicate. A communication system may in some cases be defined by the lower three layers 420, individually known as the network layer 422, the data link layer 424 and the physical layer 426.
In the OSI Reference Model, each layer is responsible for specific, defined operations in the communication process between application end users 405, 410. In furtherance of these operations, each layer may communicate information with the layers above and below it through defined interfaces (although there is not always a definitive separation between layers). Thus, for example, the transport layer may operate independently of the specific operational details of the network layer 422, the data link layer 424, and the physical layer 426 below it. The set of lower layers 420 thus operates as a transparent data pipeline to an application end user connected to the system at the transport layer interface.
FIG. 4B illustrates a flow of data between layers such as may occur during communication between two application end users. As shown in FIG. 4B, information may be passed between like layers (e.g., the transport layer in the FIG. 4B example) of each end user through a path ultimately connected at the physical layer 426. The rules that govern how data is passed between like layers at each end user are collectively referred to as a "peer-to-peer protocol." A variety of different application end users operating with different peer-to-peer protocols may communicate over a communication system so long as each application end user presents the proper upper layer interface to the communication system. Conversely, an application end user may connect with any communication system having a compatible lower layer interface.
Additional details regarding the OSI Reference Model may be found in "Telecommunication Networks" by Mischa Schwartz (Addison-Wesley Publishing Co., 1987).
One class of digital communication systems provides wireless data communication connections to stationary or mobile user stations (e.g., handsets). Examples of such wireless mobile communication systems include public safety radio systems, cellular telephone systems, and personal communication systems (PCS). A wireless communication system may include a number of base stations for completing communication paths with the user stations. The base stations may be connected to a network, either directly of via a switch.
In many mobile communication systems it is desired that user stations have the ability to initiate and receive telephone calls. By connecting a communication system to a public switched telephone network (PSTN), a user station may generally communicate with any telephone connected to the telephone network. Alternatively, a communication system may access the telephone system through an intermediate communication system such as the Global System for Mobile Communications (GSM).
In operation, it is often necessary to pass signaling information among various components of a communication system. Signaling information may, for example, comprise control messages relating to the operation of the communication system. An example of signaling information is a message from a user station to a base station indicating a malfunction. One difficulty with the user of signaling information is that it must be distinguished within the system from data communication (i.e., information intended solely for the application end user), and must be extracted by the system component needing the signaling information to perform its tasks.
The transfer of necessary control and data information can be difficult within certain types of wireless systems. For example, in a time division multiple access (TDMA) system, wherein a base station communicates with a plurality of user stations (typically mobile) in a different time slots, the amount of information that can be transferred between the base station and the user station in a given time slot is necessarily limited. In contrast, a network to which a call is connected often transfers information in large data blocks (e.g., 64 kilobyte segments). The base station should have the capability of supporting data transfers and control functions required by the network, while at the same time supporting the transfer of information and control messages to the user station over a TDMA channel.
It would be advantageous to provide a mobile communication system with an improved method of communicating both user and signaling data among system components. It would be further advantageous to provide a mobile communication system having the characteristics of a layered architecture so as to provide a transparent data pipeline to application end users.